On Tue, Jul 30, 2013 at 8:36 PM, Aaron Lu <aaron.lwe@xxxxxxxxx> wrote: > On 07/31/2013 08:11 AM, Felipe Contreras wrote: >> On Tue, Jul 30, 2013 at 6:13 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: >> >>>> If 0 turns the screen off with the intel driver, 0 should turn the >>>> screen off with the ACPI driver, having inconsistent behavior >>>> depending on which driver is used is a bug. >>> >>> The ACPI driver simply exposes and interface to interact with the AML methods >>> in the BIOS directly. >> >> No, the ACPI driver is exposing a backlight interface, which has a >> defined stable API. >> >> Documentation/ABI/stable/sysfs-class-backlight >> >> Yes, the interface doesn't define what should happen at 0, that is a >> bug in the interface definition. >> >> *How* it achieves that is an implementation detail. >> >>> Yes, this is a mistake and shouldn't be designed this way. >>> >>> However, incidentally, this makes backlight control work on your machine. >>> >>> Anyway, we need all backlight drivers to work consistently and don't tempt me >>> to rip the ACPI driver entirely from the kernel for what it's worth. >> >> Yes, they should work consistently, and go ahead, rip the ACPI driver, >> *then* you'll see many more people complaining about the Linux kernel >> breaking user-space, which should never happen. Mistakes happen, but >> if you do this willingly and knowingly, I think there would be >> repercussions for you. >> >>> Yes, that will break backlight on your system and *then* you can complain to >>> Linus if you wish. >> >> It is already broken in v3.11-rc3, in fact I just booted that to try >> it out and it booted with the screen completely black (fortunately I >> knew exactly what to type to change that). > > That is bad, can you please file a bug for that? I'll need to take a > look at your ACPI tables, thanks. File a bug where? >> Apparently this commit also needs to be reverted: efaa14c (ACPI / >> video: no automatic brightness changes by win8-compatible firmware). >> In this machine it makes the backlight work again (without >> acpi_osi="!Windows 2012"), but by doing so the ACPI driver also turns >> off the screen completely at level 0. Also, each time I change the > > So with rc3 and commit efaa14c reverted, when you set level 0 to ACPI > video's backlight interface, the screen will be off now? And this is not > the case in 3.10, right? No, setting level 0 turns it off if efaa14c is *not* reverted. In 3.10 0 doesn't turn it off. >> backlight level from X, the screen blinks as if going 100%, 0%, and >> then the desired level. > > Please attach acpidump output to the to be opened bugzilla page, thanks. I looked at the code in the DCDT, it appears to me that they store different levels depending on the OSI version, so I don't think the problem is in the ACPI driver. Yet, the issue remains there. -- Felipe Contreras -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
